STUDY OF THE REARRANGEMENT OF CYCLONONATETRAENYL(DIPROPYL)BORANE TO 7,8-DIPROPYL-7-BORABICYCLO[4.2.2]DECA-2,4,9-TRIENE BY NMR-SPECTROSCOPY

Using NMR spectroscopy it was found that at ambient temperature 9-cycl onenatetraenyl(dipropyl)borane (1) rapidly rearranges to give 7,8-dipr opyl-7-borabicyclo[4.2.2]deca-2,4,9-triene (2), ndo-9-dipropylborylbic yclo[6.1.0]nona-2,4,6-triene (3a), and two isomeric boranes with dihyd roindene skeletons (4a,b) (the ratio 2 : 3a : 4a,b is 10 : 1 : 2). exo -9-Dipropylborylbicyclo[6.1.0]nona-2,4,6-triene (3b) is an intermediat e product of the rearrangement; it is formed as a result of 8 pi-elect rocyclization in E,Z,Z,Z-cyclononatetraenyl(dipropyl)boran 1a. The tra nsformation of bicycle 3b to final product 2 occurs apparently via a s ynchronous exchange of the groups at the B atom (the transformation of the cyclopropane ring to the boracyclobutane ring accompanied by simu ltaneous migration of the propyl group from the B atom to the alpha-C atom). Borane 6 formed in this rearrangement rapidly isomerizes to 2 v ia a [1,3]-B shift.